The present invention refers, in a general way, to mechanical vibrators with a short shaft mounted inside closed or semi-closed boxes or casings, usually used in pairs and individually installed on sideplates of vibrating equipment with linear, circular and elliptical motions, either for screening, classification, transportation, dosing, feeding or simply vibration.
In a more specific way, the invention refers to a vibrator of the type that includes a bearing housing provided with external flanges for fixing the vibrator to sideplates of the equipment and supporting, through bearings, a determined portion of a shaft carrying counterweight means and being connectable to a motor unit and/or to other mechanical vibrator.
One of the most well known solutions to move vibrating screens with circular motion includes the provision of a mechanical vibrator, basically comprises of a single elongated shaft, transversally disposed in order to have its end portions journaled through respective bearings on opposite sideplates of the equipment and projecting outwardly therefrom for having its ends carrying respective counterweights.
One of the ends of the single shaft is provided with means for coupling to the motor unit is as shown in FIG. 1.
This prior art construction, despite apparent simplicity, presents a series of inconveniences, such as:
Since the shaft is long and heavy, it is flexible, thereby adversely affecting the bearings;
The use of bearings of large dimensions is required;
The assembly and disassembly of bearings must usually occur at the site, which could be a high pollution environment.
In order to minimize the above-mentioned problems, compact universal vibrators were developed, as per FIG. 2, composed of a rigid bearing housing with a pair of bearings and incorporating an external middle flange for fixing to respective sideplates of the equipment. The bearings support a short shaft with opposite ends carrying respective adjustable counterweights, one of which stays inside the respective sideplate of the equipment.
The first prior art mechanism, with a long transversal shaft, was then replaced by a pair of compact universal vibrators, each one being mounted on respective sidewalls or vibrating screen (or other similar equipment) and connected to another vibrator through a portion of a flexible connecting shaft, as per FIG. 3.
Each compact vibrator of the prior art can be replaced as a sealed assembly or package, permitting maintenance in proper area.
In a compact vibrator, of the type mentioned above, load distribution on two bearings instead of usual one in a long shaft arrangement reduces bearing diameters and permits higher rotation speed. Cost and weight of compact arrangement of the type mentioned above are significantly lower than those of known long shaft arrangements, with consequent improvement in maintenance conditions. Nevertheless, despite presenting several advantages over long shaft arrangements, the known compact arrangement (with short shaft) of the prior art introduced some limitations that did not exist in the classic arrangement of long transversal shaft, which includes:
The occupation of a larger internal space of screen (or other equipment) than that required for the classical solution of long shaft;
The setting of the eccentric mass to be effected also inside the equipment, since the counterweights are on both sides of the respective sideplates, of the equipment.
The ideal would be to use a compact vibrator of the prior art, as per FIG. 4, but with setting of eccentric weights only on external sides of the respective sidewalls of the equipment. However, mechanical viability of this arrangement, as per FIG. 4, is highly reduced. It should be noticed that on a balanced situation, as per FIG. 4, no bending moment Mo is applied on the sideplate, since: EQU F1.multidot.L1=F2x.multidot.L2 ##EQU1## EQU Mo=0
The presence of adjusting weight (Q) only on one side, that is, on the external side, creates an unbalanced situation, as shown in FIG. 5, where: EQU F'1&lt;F1 EQU F'1.multidot.L1&lt;F2.multidot.Ls EQU R1&lt;R2 EQU Mo/=0=F2.multidot.L2-F'1.multidot.L1
Forces R1 and R2 on the bearings, instead of being equally distributed, as in case of the compact vibrators of FIGS. 2 and 3, are different and amplified.
A bending moment Mo also appears in relation to the sideplates, once equilibrium of bending moments in relation to the center of the mechanism was destroyed. Such bending moment occurrence is unacceptable to the sidewall or sideplate of any vibrating screen or similar equipment.